1. Field of the Invention
The present invention relates to a disc player and, more particularly, to a disc player suitable for use in reproducing a CD-ROM used as a medium for storing data and programs.
2. Description of Related Art
In a CD-ROM (Compact Disc Read-Only Memory) reproducing apparatus, rotational control is performed by setting a target rotational speed of a spindle servo always to the frequency of a frame synchronization signal of 7.35 KHz or an integral multiple thereof. A PLL (Phase-Locked Loop) circuit for generating a clock based on which an EFM (Eight-to-Fourteen Modulation) signal reproduced from a disc is processed is constituted such that the center frequency of the PLL circuit is set to a channel clock of the EFM signal to be generated when the spindle rotational speed is equal to the target rotational speed. Such a setup allows the CD-ROM reproducing apparatus to read data from the disc when the spindle rotational speed has approached the target value and has entered a capture range of the PLL circuit.
In the spindle servo control described above, a servo error signal is generated from the EFM signal. That is, servo control is made so that the difference between a time interval and a target value of a reproduced frame synchronization signal becomes zero. Therefore, when an information reading optical spot radiated from an optical pickup (hereinafter referred to simply as a pickup) has traversed recording tracks (namely, recording pit trains) on the disc, the time interval of the reproduced frame synchronization signal becomes inaccurate because of the spot's crossing a mirror surface between tracks and the discontinuation of the EFM signal, thereby failing the correct control of spindle servomechanism.
Meanwhile, one important performance characteristic of the CD-ROM is a seek time in which the pickup is moved to a next data read position. Since the CD-ROM player has only one pickup, the pickup can begin to move only after reading data at a position, at least requiring a time for the movement. This restricts any shortening of the seek time. In addition, as described above, spindle servomechanism cannot be controlled precisely during a traverse time Data can be read from the disc only when the spindle rotational speed has approached a target value and has entered the capture range of the PLL circuit, thus requiring a time to some extent for the pickup to reach a next read position to be able to read data.